Atherosclerosis is a common human ailment arising from deposition of fatty-like substance, such as atheroma, or plaque on the walls of major blood vessels. These deposits occur within the peripheral arterial system which feeds the limbs of the body and also occur within the coronary arterial system which feeds the heart. These deposits accumulate in localized areas, narrow the vascular lumen, and eventually causing restriction of normal blood flow. In some cases, the deposits result in a chronic partial or total occlusion. Such restriction can lead to a serious health risk including critical limb ischaemia. If blood flow cannot be adequately restored through surgical or endovascular intervention and the probability of limb amputation increases dramatically.
Until recently, chronic total occlusions have been treated by bypass which poses high procedural risks and is quite traumatic to the patient. Recently, catheter based intravascular procedures have been utilized. These techniques include step-by-step crossing of an occlusion using Excimer laser atherectomy devices and methods, crossing the occlusion with highly flexible and maneuverable guide wires, and other techniques known in the art. Once the lesion has been crossed, then standard endovascular devices such as laser atherectomy, angioplasty, stenting, and the like, can be used to enlarge the lumen and increase blood flow within the peripheral arterial system. These catheter-based intravascular procedures are typically preferred since they are much less traumatic to the patient, safer and cost-effective while delivering comparable long term vessel patency compared to more traumatic surgical alternatives.
Before catheter-based treatments can be used, with the exception of step-by-step Excimer laser methods, the guide wire must first pass through the total occlusion to provide access for the interventional catheter. Specifically, once a guide wire has crossed the occlusion, it can then be used as a rail to support interventional catheters. In some cases, the physician can maneuver the guide wire through the total occlusion establishing access. In many instances, the physician encounters a calcified cap on the proximal end of the occlusion and is unable to maneuver the guide wire through the cap and across a calcified or fibrous lesion. In many cases, the guide wire inadvertently penetrates the subintimal space between the intimal layer and the adventitial layer of the blood vessel as the guide wire attempts to cross the lesion. Once in the subintimal space, it is difficult to direct the guide wire back into the vessel lumen making it nearly impossible to perform a catheter based intravascular procedure.
In one related art technique, Dr. Bolia developed a revasculature procedure as described in Recanalisation offemoro-popliteal occlusions: Improving success rate by subintimal recanalisation, Clinic Radiol, 40:325, 1989, by exploiting the subintimal space where a guidewire enters the subintimal space between the intima and adventitia layers, is subsequently advanced to a point distal to the occlusion, and then maneuvered to re-enter or puncture the vessel layers to enter the true lumen of the vessel. Once the guide wire has traversed through the subintimal layer and re-enters the true lumen of the vessel at a point distal to the occlusion, percutaneous balloon angioplasty is performed to restore blood flow through subintimal recanalization. This is a highly skilled technique with a low to moderate success level of consistent re-entry at the physician's preferred location just distal to the occlusion.
There are number of other related art catheters and methods for forming lateral penetrations through tissue to and from blood vessels past total occlusions, some of these are described in U.S. Pat. Nos. 5,443,497; 5,429,497; 5,409,019; 5,287,861; 6,231,546; 6,217,527; 6,506,178; 6,221,049; 6,235,000; 6,511,458; 6,719,725; 7,004,173; and 7,179,270, all of whichare incorporated by reference for teaching reentry catheters, methods and for the purpose of written description and enablement requirements. These related art methods embody penetration of a needle exiting through either a side port or through a distal port, the needle must be oriented properly to ensure that the needle, when deployed, re-enters at a preferred location distal to the occlusion. One problem with these methods is a tendency of the catheter to back out as a result of the moment imposed by force required to penetrate the subintimal layers to gain access to the vessel true lumen. This is particularly problematic in the presence of calcified lesions causing an increase in the forces necessary for successful re-entry and, in many cases, requiring the physician to re-enter at a sub-optimal location.